1. Technical Field
The present invention relates to a MEMS resonator and a manufacturing method thereof.
2. Related Art
In recent years, MEMSs have exhibited a favorable growth in the usage thereof for apparatuses such as acceleration sensors and video devices. MEMS is an acronym of Micro-Electro-Mechanical System, and there are various interpretations for what encompassed within the conceptual range thereof. Generally, it means, “fine functional devices produced using semiconductor manufacturing techniques”, while in some cases, it is also referred to as “micro machine”, or “micro system technology (MST)”. Those devices are manufactured based on fine processing techniques developed for fabrication of semiconductors. Currently, MEMSs are manufactured individually, or, produced onto the integrated circuit (IC) in a process after the manufacturing thereof.
Along with the trend of semiconductor devices becoming smaller and are formed in higher integration, through holes or contacts holes (hereinafter simply referred to as “holes”) are made finer; hence a high reliability is required in metallization. Therefore, those holes require a higher coverage ratio of wiring metal. A semiconductor device manufacturing method has been suggested which improves the coverage ratio of the wiring metal, in the case where the aspect ratio of holes such as through holes or contact holes is large. The method includes: a process for forming in advance a stopper film in a vicinity of the bottom of a hole to be formed, in a location surrounding the hole; and a process for forming a sidewall on the internal wall of the stopper film. JP-A-5-6891 is an example of related art.
Moreover, in a method for manufacturing a semiconductor device such as an insulation gate type device having a thick field oxide film, if the processed shape of the field oxide film is deficient, wire thinning occurs in the gate electrode or in the main wire through which a main current flows at a tapered edge of the field oxide film, the wire being composed of Al and the like. In an extreme case, a step disconnection of wire occurs, significantly impairing the reliability of electrode wirings. In order to reduce the occurrences of such problem, a semiconductor manufacturing method is suggested, in which a taper at an arbitrary angle meeting the thick field oxide film is easily formed and a control over the taper angle processing is improved. JP-A-7-66280 is an example of related art.
Sidewall-shaped etching residue in a MEMS structure of a MEMS resonator has been either removed by slightly strong over etching, or, left as it is. In the coming years, it will be necessary to flatten the MEMS structure in a MEMS process performed simultaneously with an IC manufacturing. Therefore, if the occurrence of the sidewall-shaped etching residue in the MEMS structure can be prevented, the reliability of the MEMS resonator can be increased.